Message-ID: <20141124180222.GA1449@developer>
Date:	Mon, 24 Nov 2014 14:02:25 -0400
From:	Eduardo Valentin <edubezval@...il.com>
To:	Lukasz Majewski <l.majewski@...sung.com>
Cc:	Zhang Rui <rui.zhang@...el.com>,
	Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>,
	Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>,
	Linux PM list <linux-pm@...r.kernel.org>,
	Vincenzo Frascino <vincenzo.frascino@...com>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Lukasz Majewski <l.majewski@...ess.pl>,
	Nobuhiro Iwamatsu <iwamatsu@...auri.org>,
	Mikko Perttunen <mperttunen@...dia.com>,
	Stephen Warren <swarren@...dotorg.org>,
	Thierry Reding <thierry.reding@...il.com>,
	Alexandre Courbot <gnurou@...il.com>,
	linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org,
	Viresh Kumar <viresh.kumar@...aro.org>
Subject: Re: [PATCH v2] thermal:core:fix: Check return code of the
 ->get_max_state() callback


Hello Lukasz,

On Mon, Nov 24, 2014 at 11:38:54AM +0100, Lukasz Majewski wrote:
> Hi Eduardo,
> 
> > 
> > Lukasz,
> > 
> > On Tue, Nov 18, 2014 at 11:16:30AM +0100, Lukasz Majewski wrote:
> > > The return code from ->get_max_state() callback was not checked
> > > during binding cooling device to thermal zone device.
> > > 
> > > Signed-off-by: Lukasz Majewski <l.majewski@...sung.com>
> > > ---
> > > Changes for v2:
> > > - It turned out that patches from 1 to 6 from v1 are not needed,
> > > since they either already solve the problem (like imx_thermal.c) or
> > > not use cpufreq as a thermal cooling device.
> > > - The patch 7 from v1 is also not needed since this patch on error
> > > exits this function without using max_state variable.
> > > - In thermal driver probe the cpufreq_cooling_register() method
> > > presence is crucial to evaluate if the thermal driver needs any
> > > actions with -EPROBE_DEFER.
> > 
> > Have you tried this patch with of-thermal based systems?
> 
> Yes. I did try it with Exynos (after the rework). And there weren't
> any regressions.
> 
> To be precise - do you refer to of_cpufreq_cooling_register() [1] or
> cpufreq_cooling_register() [2]?
> 

[1]

> For the latter [2] - drivers like imx_thermal.c are fully prepared for
> -EDEFER_PROBE.
> 
> For the former [1] - only cpufreq-dt.c uses it (and Exynos SoC after
> the rework).
> 
> > 
> > The above proposal works if the thermal driver is dealing with loading
> > cpu_cooling. But for of-thermal based drivers, the idea is to leave to
> > cpufreq code to load it. 
> 
> I assume, that you mean case [1]?
> 

yup

> > 
> > As an example, I am taking the ti-soc-thermal, but we already have
> > other of-thermal based drivers. Booting with this patch ti-soc-thermal
> > (of-based boot) loads fine, but the cpu_cooling never gets bound to
> > the thermal zone.
> 
> Could you share the exact SoC/board/_defconfig setup to reproduce this
> behavior? I possess Beagle Bone Black, but it doesn't have thermal
> support (perhaps because its lack of accuracy).
>

Well, it may happen any system a driver with of-thermal + cpufreq-dt.

One board that is easily available is OMAP4460 panda board (tried
myself, the problem is there).

> With my Exynos setup I didn't experience any problems with this patch.
> 
> > 
> > The thing is that the bind may happen before cpufreq-dt code loads the
> > cpufreq driver, and when cpu_cooling is checking what is the max freq,
> > by using cpufreq table, it won't be able to do it, as there is no
> > table.
> 
> As I look into the cpufreq-dt.c driver - in the cpufreq_init()
> function, the call to of_cpufreq_cooling_register() is performed just
> before cpufreq_table_validate_and_show().
> It looks like a mistake in the cpufreq-dt.c code.
> 

Well, I believe for our case, better would be if the cpu_cooling could
be done after cpufreq driver registration call.


> > 
> > While, without the patch, it will use wrong in the binding, but after
> > it gets bound, and cpufreq loads, the max will be used correctly.
> 
> Correct. Such _wrong_ behavior was the original motivation to prepare
> this patch.
> 
> > 
> > And in this case, the system still works besides this bug. 
> 
> Unfortunately there is also a "window" in which the driver is not
> properly configured and can cause system crash, although it is unlikely.
> 

Agreed.

> 
> > The
> > reasoning is because the max state comes from DT (2) and lower and
> > upper wont be equal to THERMAL_NO_LIMIT. Then, the following check
> > will use the parameter, instead of max_state:
> > 
> >         cdev->ops->get_max_state(cdev, &max_state);
> > 
> > 	/* lower default 0, upper default max_state */
> > 	lower = lower == THERMAL_NO_LIMIT ? 0 : lower;
> > 	upper = upper == THERMAL_NO_LIMIT ?
> > 				max_state : upper;
> > 
> > In summary, introducing this patch, although it fix a problem, will
> > introduce regressions, in of-thermal based drivers.
> 
> To be more precise - it will affect systems, which use of-thermal.c and
> cpufreq-dt.c in the same time, due to wrong ordering in the latter file.
> 

Exactly.

> Could you give me a hint about the exact affected system? I've grep'ed
> for CPUFREQ_DT in the ./arch/arm/configs with no success.
> 

Yeah, the grepping is correct. But well, just because it is not in
defconfigs does not mean it won't be used. 

> > 
> > I believe, to have this fix, you need to provide a way to have probing
> > deferring also in cpu_cooling. That needs also the change in the
> > cpufreq driver, as I mentioned in the other thread.
> 
> I will think about possible solution and refer to previous discussion. 
> 

Good. For your patch, it is still sane to have it. But needs to be taken
after fixing the ordering between cpufreq-dt and cpu_cooling.


> > 
> > Cheers,
> > 
> > > ---
> > >  drivers/thermal/thermal_core.c | 6 ++++--
> > >  1 file changed, 4 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/drivers/thermal/thermal_core.c
> > > b/drivers/thermal/thermal_core.c index 43b9070..8567929 100644
> > > --- a/drivers/thermal/thermal_core.c
> > > +++ b/drivers/thermal/thermal_core.c
> > > @@ -928,7 +928,7 @@ int thermal_zone_bind_cooling_device(struct
> > > thermal_zone_device *tz, struct thermal_zone_device *pos1;
> > >  	struct thermal_cooling_device *pos2;
> > >  	unsigned long max_state;
> > > -	int result;
> > > +	int result, ret;
> > >  
> > >  	if (trip >= tz->trips || (trip < 0 && trip !=
> > > THERMAL_TRIPS_NONE)) return -EINVAL;
> > > @@ -945,7 +945,9 @@ int thermal_zone_bind_cooling_device(struct
> > > thermal_zone_device *tz, if (tz != pos1 || cdev != pos2)
> > >  		return -EINVAL;
> > >  
> > > -	cdev->ops->get_max_state(cdev, &max_state);
> > > +	ret = cdev->ops->get_max_state(cdev, &max_state);
> > > +	if (ret)
> > > +		return ret;
> > >  
> > >  	/* lower default 0, upper default max_state */
> > >  	lower = lower == THERMAL_NO_LIMIT ? 0 : lower;
> > > -- 
> > > 2.0.0.rc2
> > > 
> 
> 
> -- 
> Best regards,
> 
> Lukasz Majewski
> 
> Samsung R&D Institute Poland (SRPOL) | Linux Platform Group

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